when studios do stunt scenes with cars they usually remove parts like engine tranny drive shafts etc im not absolutely sure thats its for weight or safety probably both you can notice this in many stunt or crash scenes most cars in these scenes are being towed by cable to a rail causing it to roll over and are sometimes fitted with a large ram used to cause the cars to flip the studios will even go as far as modifying junk cars or building replicas of very expensive cars and now with cgi the stunts will only be getting better and more detailed movie magic